Means for shielding and cooling reactors



Feb. l

Filed oct. a, 1946 E. P. wlGNER Erm.

nited States Pater MEANS FOR SHIELDING AND COOLING REA'CTORS Eugene P.Wigner, Oak Ridge, Tenn., Leo A. Ohlinger,

Chicago, lll., and Gale J. Young and Alvin M. Weinberg, Oak Ridge,Tenu., assignors to the United States of America as represented by theUnited States Atomic Energy Commission Application octobein s, 1946,serial No. 701,910 s claims. (Cl. zoe-193.2)

This invention relates to neutronic reactors, and, more particularly, toa novel method and means for shielding reactors to protect operatingpersonnel from emanations such as neutrons, and alpha, beta, and gammaradiations. The instant application is a continuation-in-part ofcopending application, U. S. Serial No. 681,252, filed July 3, 1946, nowpatent No. 2,770,591, issued on November 13, 1956.

In neutronic reactors, a neutron such as U2, U235, or 94239, or mixturesthereof, is subjected to fission by absorptionk of neutrons, and aselfsustaining chain reaction is established by the neutrons evolved bythe ssion. In general such reactors comprise bodies o-f compositionscontaining such iissionable material, for example, natural uranium,disposed in a neutron slowing material which slows the neutrons tothermal energies. Such a slowing material is termed a neutron moderator.Carbon, beryllium, and D30 (heavy water) are typical moderators suitablefor such use. Heat is evolved during the reaction which is removed bypassage of a coolant through the reactor -n heat exchange relationshiptherewith. v

An object of the present invention is to provide a novcl shield for usewith a neutronic reactor, such as above described, said shieldcomprising ya contained quantity of two immiscible hydrogeneous liquidsof different speciiic gravity whereby the lighter liquid oats on theheavier liquid.

Another object of the invention is to provide a novel method and meansfor shielding a body of coolant after having passed through a neutro-nicreactor.

It may be noted that the term hydrocarbon fluid, as used herein, ishereby broadly defined to include aromatic compounds as Well asaliphatic compounds, Iboth saturated and highly conjugated.- Such ashield is advantageous in producing a minimum amount of explosive gasunder neutron bombardment, and it has been discovered that ordinarystraight chain hydrocarbons are effective and conjugated double-bondhydrocarbons are highly effective in reducing the production o-fexplosive gases.

It may also be noted that the invention comprehends a radiation shieldof vhighly polymerized aromatic or ali' phatic compounds such as thoseproduced by the bombardment of benzene, biphenyl and their compoundswith high speed particles, such as electrons, deutero-ns or neutrons;and it will be understood that the neutron bombardment of a shieldingfluid, such as biphenyl, associated with a neutronic reactor produces ahighly polymerized compound which is particularly resistant topenetration by radioactive emanations from the nuclear fission chainreaction.

In addition other hydrocarbons may be used as a iiuid shield includingoctane, isooctane, heptane, hexane, methane, ethylene, propylene,butylene, xylene, toluene, or the polymers or other products formed bybombardment of these compounds with neutrons, deuterons, or electrons.

The foregoing and other objects and advantages of ssionable isotope,

2,373,243 Patented Feb. 10, 1959 Describing the invention in detail, andreferring yto `ak illustrated in the drawing,

preferred embodiment thereof, the neutronic reactor 10 comprises acontainer or reaction tank 11 which is vertically pierced with arelatively large number of conduits or tubes 12 preferably of aluminum,only four of which are shown diagrammatically, said tubes enclosingnatural uranium rods 14 preferably covered with a sealed protectivealuminum jacket and `being surrounded by heavy water 16 which serves asa neutron moderator.

A shield tank 18 is provided above the reactor 10 and contains a clearfluid such as water 20 immediately above the reactor, and a clear lowVolatility hydrocarbon liquid 22 oating on the water 20. The tubes 12open through the reaction tank top 13 into the shield tank 18 and aresupplied through the lower ends thereof from a cooling water supplyheader 24 into which cooling water may be forced Iby a pump 26 from aAsource of cooling water not shown. The cooling water introduced throughthe header 24 flows upwardly through the tubes 12, around the uraniumrods 14, and into the shield tank 18 from `which it is withdrawn throughorifices 27 leading to a discharge header 28 surrounding the shield tank18 and from which the discharge water may be withdrawn through a pipeline 30. A closed system for the water 20 may be employed if desired.The reaction tank 11 is only partially iilled with the heavy watermoderator 16 for purposes of controlling the neutronic reactionreproduction ratio within a range above and below unity as laterdescribed in greater detail, from a heavy water reservoir 32, the levelof heavy water 34 in the reservoir being determined by the maximumrequirement for heavy water in the reaction tank 11. More particularly,the heavy water reservoir may be maintained under pressure and the heavywater may 'be introduced to the reaction tank through a pipe line 36under control of a valve 38. Excess heavy water may be pumped from thereaction tank 11 to the reservoir 32 by a pump 40 operating through apipe line 42 and valve 44.

The effective size of the reactor 10 is determined by the quantity ofheavy water in the reaction tank 11 and since an excessive quantity ofheavy Water in the reaction tank 11, over and above critical sizeconditions, may result in a rapid exponential rise in neutron density,means are provided for dumping the heavy water rapidly from the tank 11in the form of a number of emergency pipe lines 46 connected between thebottom portion of the reaction tank 11 and a heavy water outlet header48 leading to the heavy water reservoir 32. Each of the emergency pipelines 46 is provided with a safety control valve 50 maintained in aclosed position lby gas pressure applied through pipe lines 51 from theheavy water reservoir 32. Such pressure is preferably maintained lbyhelium gas introduce-d to the heavy water reservoir 32 through a pipeline 52 and valve S4 from a helium reservoir 56.V *During reactoroperation, the valve 54 is maintained in an open position by a valvelever S8 connected to a control rod 60, and in the event that rapiddumping of the heavy water in the reaction tank 11 is desired, thehelium pressure in the reservoir 32 may be reduced rapidly by openingthe reservoir to the atmosphere through a line 62 by opening a valve 64also operated by control rod 60. Release of pressure in the reservoir 32likewise releases pressure in the pipe lines 51 connected to the dumpvalves 50 causing them to open and the heavy water moderator 16 to bedumped rapidly into the reservoir 32. Thus when one valve, such as thevalve 64 is in a closed position the other, such as valve 54, is in anopen position.

During operation, the reaction tank 11 is maintained onlypartiall'ylled'with the heavywater 1'6" leaving a space 63 above the heavy waterfor release of gases therefrom produced during operation of theVreactor,..although,.

itis tolh'e'u'nderstoodthat during operation ofthe 'reactor the'leve'lof tne'h'eavy water recovers tneluraniumrrod'st gaseousdecomposition products that' 'are Ventedthrough.

an exhaust pipe line 74. Since the decomposition products, arepredominantly deuterium and oxygen these gases may be recombined inarecombination chamber 'i6 con nected to the exhaust pipe line 74.Therecomhination.

chamber 7t'may enclose a catalytic agent such as platinizedcharcoalmaintained at an elevated temperature or ahot grid over which the gasesare drivenby lthe helium to 'be recomhined'ihto heavy water vapor. Suchvapor is withdrawn from vthech'amb'er 76 through a pipe line 78j andled; to a heavy water condenser 'Sil for condensation of the vapor,whereupon the condensediheavy water is returned 'tothe reservoir 32through a line SZ, heavy water purien S23, andlline 36. The condenser 80is cooled by va fluid medium such as water introduced theretothroughinlet' line 88, andiwithdrawn through anoutlet 9); The helium iswithdrawn from the condenser 80 through a line 92^leading to a heliumpurifier 94 where other gaseous products that may he formedlin thereactor are removed,l whereupon the helium is returnedthrough` a pipeline 9`and'pump 98 to the helium reservoirv S16.y

l'n the operationvotthe` system shown and so far sescribed,z theneutronic reactionwithin the reactor- 10develops considerableV energy inthe form of beta and gamma raysA as well' as kinetic energy from thetission products; A great portion otv this energy is released within thetubes l2 extending vertically through the re.- action tankV 11 and'. isabsorbed, by the ilow of water through these tubes around theuraniumrods 1d. However, some of the neutrons developed in the reactor,as well as highintensity gamma rays, escape therefrom and may result ina great' health hazard to operatingpersonnel'. With the above-describedarrangement of the water and hydrocarhon fluid-inthe shield tank` 18,pro tection is otered' for operating personnelabove the neutroni'creactor, although it is preferredv to provide side shieldingVcor'npletc-:l'y surrounding other surfaces of there actor.Consequently, thereactor isplacedjhetweentheavy sidey shields (.not.,shown)4 so that operating personnel may approachihe equipment forAservicingpurposes.

It Willhev notedtr'om thcsabovedescription that the upper faceofthereactorl can be opened to the, atmosphere through the two superimposedliquid layers. These two layers. can form thenormall topfshieldlduringoperation, andlinaddition provide a .space wherein vthe uranium rodscan-'beremovedunder the: protection of the liquid if dcsired, althoughsuch removal is no part of the present invention. It' is 'p/efd' SISOthat the Coolant he made to ow upwardly so that if affailure of thecoolant supply occurs, the coolant can reverse its ow by gravity anddrain out for a short time through the coolant tubes, thereby coolingthe uranium-'rods' for a critical period in which delayedtneutronsarebeing-,emittcd, after shutdown of the chain reactionhasybe'enihitiated. However, the main feature of the present inventionis that in case of failureoff amalnminu'rnjjacket'to maintain a seal,whereby uraniumf'rcmthe 'rods and/ orradioactiveiission .productsenter.the-coolant stream, the superimposedlayer ot' hydrocarbon reduces theintense radioactivity introduced into the layer over the reactor, andpermits removal of the oi'e'ndin'g rod by personnel shielded byf-theluncontaminated hydroearbonlayer. Thusgby the use of the hydrocarbonlayer, a rod having a leaking jacket can be removed `a short timeaftershutdownwithout having to waitif'or'tlie radiationjn the coolant layerto decay over along period 'ofv time.

It will 'he understoodthat-th'e above-described' embodil mentgot` theinvention is diagrammatic and an operative reactor of' this type Amay beconstructed in accordance with the teachings' ofFigs; Zand 3 and theaccompanying specification of theabove-me'ntoned copending applica?tion.

While-thc vtheory of'nuclear reactions set forthherein is based onithebest' presently known experimental evidence,

the inventiom is not' limited thereto, inasmuch as. addi-- tionalexperimental data later discovered may modify the theory disclosed.

Obviously, many modifications may oe made in the specific embodimentdisclosedv withouttdeparting from the' intended scope ofv theinvention'wliich is limited only by the appended claims.

What is clairnedis:

l. ln a system of the class desc1'1'bed`,kmealns for-sus'- tainin'g anuclearilssion chain reaction comprising heavy water having verticalpassages therethrough and thermal. neutron tissionable material in saidpassages, 'a coolant' llcwi'ng through said passages andintoa'co'ntaineitahove the passages, and@A hydrocarbon shielding uido'atingon the coolant abovethe passages.

7.. Ther system oflclaim lin* which the' neutron mod= erator is heavywater, the''ssiona'blematerial is uranium,

the coolant is water, and the hydrocarbon shielding iluid is anaromatichydrocarbon.

3. The'systern ot" claim 2'* irl-which the aromatic is biphenyl.

Reterences lited inI the lle^-of thisl patent- Foiusrorr PATENTS France.t Oct. 28, 1,9740, Switzerland-.-.ma Oct. 2, 1,944'

GTI-IER KEPRENGES Deming: LGeneral Chemistryfrded. p. 148 (1930) lohnWiley &,Sons.

Smyth: Atomic Energy `for Military Purposes, pp. 1G33,` 104, August1945. (Copy may be purchased from Supt. of'Documents, Washington^25tDLC.)

Kelly et ali: Phy. Rev. 73 1135;-9 (1948).

2. IN A SYSTEM OF THE CLASS DESCRIBED, MEANS FOR SUSTAINING A NUCLEARFISSION CHAINS REACTION COMPRISING HEAVY WATER HAVING VERTICAL PASSAGESTHERETHOUGH AND THERMAL FLOWING THROUGH SAID PASSAGES AND INTO ACONTAINER ABOVE THE PASSAGE, AND A HYDROCARBON SHIELDING FLUID FLOATINGON THE COOLANT ABOVE THE PASSAGES.